1. Field of the Invention
The present invention is broadly concerned with compositions and methods for lowering the pH of soil microenvironments so as to increase the micronutrient uptake of growing plants. The compositions of the invention are preferably granulated and comprise ammonium sulfate, elemental sulfur, and a micronutrient selected from the group consisting of zinc, iron, manganese, copper, boron, cobalt, vanadium, selenium, silicon, nickel, and mixtures thereof. In the preferred methods of the invention, granulated compositions are applied to the soil resulting in the formation of acidic soil micro-environments, while the soil surrounding the microenvironments retains its original pH. Such localized low pH conditions lead to an increased availability and plant uptake of the important micronutrients. In an alternative embodiment, non-granulated compositions can be utilized when it is desirable to decrease the overall pH of bulk soil.
2. Description of the Prior Art
In order to maintain healthy growth, plants must extract a variety of elements from the soil in which they grow. These elements include the so-called micronutrients zinc, iron, manganese, copper, boron, cobalt, vanadium, selenium, silicon, and nickel. However, many soils lack sufficient quantities of these micronutrients or contain them only in forms which can not be readily taken up by plants. To counteract these deficiencies, sources of the deficient element(s) are commonly applied to soils in order to improve growth rates and yields obtained from crop plants. This application has generally been accomplished using oxides, sulfates, oxysulfates, chelates, and other formulations.
In ordinary agricultural soil, pH's vary from about 4.5 to 8.3. Soils having pH's below 6.5 are normally subjected to liming to bring the pH of the soil to neutral or near-neutral. Liming is necessary for the availability of many macronutrients (such as nitrate, phosphates, magnesium, and especially calcium). However, when lime is applied, the availability of micronutrients is generally decreased due to the formation of insoluble products. This is especially true if over-liming occurs. Similarly, fields with naturally occurring pH's in excess of 7 have restricted availability of micronutrients due to the formation therein of insoluble reaction products (fixation). It is known that the availability of most micronutrients increases as the pH decreases. In the past it has been impractical to utilize the knowledge that an acid environment can provide enhanced availability of micronutrients. One reason is that, although micronutrient availability is enhanced by low pH's, maximum crop yields are normally obtainable at higher pH's.
In order to compensate for the lack of available micronutrients, many farmers apply excess amounts of fertilizers containing those micronutrients to the soil. Farmers may however apply expensive foliar applications which may solve the problems, but at a high cost to the farmer. The micronutrients (which are generally fixed or become unavailable when applied to soils) often limit the uptake of the macronutrients. The macronutrients may then wash off or leach out of the soil and contaminate the groundwater or surface water.